This invention relates to jigs which separate materials in a feed mixture on the basis of differing specific gravities and especially, but not exclusively, to centrifugal jigs of the general type described in International Patent Publication Nos. WO86/04269 and WO90/00090, in which a feed slurry is introduced into a rotating chamber bounded radially by a screen provided with ragging on its inner surface, the ragging being dilated repetitively to provide jigging action.
In WO86/04269, the ragging is dilated by pulsing the water in a hutch chamber which surrounds the screen. The water is pulsed by means of a diaphragm positioned at the base of the hutch chamber. In WO90/00090, a number of hutch chambers are circumferentially spaced about the jig screen, with the water in the hutch chambers being pulsed sequentially. Each hutch chamber has a diaphragm positioned below the screen, with the diaphragms being actuated by respective pushrods driven by a central crank assembly.